Everyone heading north on old lady's animal (5)
I believe the answer is:
llama
'animal' is the definition.
(llamas are animals)
'everyone heading north on old lady's' is the wordplay.
'everyone' becomes 'all' (all people).
'heading north' says the letters should be written backwards (in a down clue, letters travel north).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'old lady' becomes 'ma' (both can mean mother).
'all' in reverse letter order is 'lla'.
'lla'+'ma'='LLAMA'
(Other definitions for llama that I've seen before include "Camel-like wool source" , "Peruvian camel" , "S American animal related to the camel" , "South American relative of the camel" , "This could carry your stuff" .)